Re: [RFC PATCH 1/3] eeprom: Add a simple EEPROM framework

[Srinivas Kandagatla]

On 20/02/15 17:46, Russell King - ARM Linux wrote:
> On Thu, Feb 19, 2015 at 05:08:28PM +0000, Srinivas Kandagatla wrote:
> > +static struct class eeprom_class = {
> > +	.name		= "eeprom",
> > +	.dev_groups	= eeprom_dev_groups,
> > +};
> > +
> > +int eeprom_register(struct eeprom_device *eeprom)
> > +{
> > +	int rval;
> > +
> > +	if (!eeprom->regmap || !eeprom->size) {
> > +		dev_err(eeprom->dev, "Regmap not found\n");
> > +		return -EINVAL;
> > +	}
> > +
> > +	eeprom->id = ida_simple_get(&eeprom_ida, 0, 0, GFP_KERNEL);
> > +	if (eeprom->id < 0)
> > +		return eeprom->id;
> > +
> > +	eeprom->edev.class = &eeprom_class;
> > +	eeprom->edev.parent = eeprom->dev;
> > +	eeprom->edev.of_node = eeprom->dev ? eeprom->dev->of_node : NULL;
> > +	dev_set_name(&eeprom->edev, "eeprom%d", eeprom->id);
> > +
> > +	device_initialize(&eeprom->edev);
> > +
> > +	dev_dbg(&eeprom->edev, "Registering eeprom device %s\n",
> > +		dev_name(&eeprom->edev));
> > +
> > +	rval = device_add(&eeprom->edev);
> > +	if (rval)
> > +		return rval;
> > +
> > +	mutex_lock(&eeprom_list_mutex);
> > +	list_add(&eeprom->list, &eeprom_list);
> > +	mutex_unlock(&eeprom_list_mutex);
> > +
> > +	return 0;
> > +}
> > +EXPORT_SYMBOL(eeprom_register);
> > +
> > +int eeprom_unregister(struct eeprom_device *eeprom)
> > +{
> > +	device_del(&eeprom->edev);
> > +
> > +	mutex_lock(&eeprom_list_mutex);
> > +	list_del(&eeprom->list);
> > +	mutex_unlock(&eeprom_list_mutex);
> > +
> > +	return 0;
>
> There's problems with this.  "edev" is embedded into eeprom, and "edev"
> is a refcounted structure - it has a lifetime, and the lifetime of
> eeprom is thus determined by edev.
>
> What this means is that calling eeprom_unregister() and then freeing
> the eeprom structure is a potentially unsafe operation - the memory
> backing edev must only be freed when the release method for the
> struct device has been called.

Thats a good catch, Yes I see the issue.

Moving the struct eeprom_device allocation to eeprom core.c should 
address this issue. This makes eeprom self contained and can safely free 
the eeprom_device memory in eeprom_class.eeprom_release().

Will fix this in next version.

> > +struct eeprom_device {
> > +	struct regmap		*regmap;
> > +	int			stride;
> > +	size_t			size;
> > +	struct device		*dev;
>
> Failing to understand and address the driver model life time issues is
> a major blocker for this patch.  Sorry.
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